Pin macos CI to macos-11 (#50)

Author: johnthagen

.github/workflows/build.yml

@@ -7,7 +7,8 @@ jobs:
     name: Default
     strategy:
       matrix:
-        platform: [ ubuntu-latest, macos-latest, windows-latest ]
+        # TODO: Fix libc build issues on macos-latest, which is now macos-12.
+        platform: [ ubuntu-latest, macos-11, windows-latest ]
         toolchain: [ stable, 1.28.0, nightly ]
     runs-on: ${{ matrix.platform }}
     steps:
@@ -21,7 +22,7 @@ jobs:
     name: no_std
     strategy:
       matrix:
-        platform: [ ubuntu-latest, macos-latest ]
+        platform: [ ubuntu-latest, macos-11 ]
         toolchain: [ stable, 1.30.0, nightly ]
     runs-on: ${{ matrix.platform }}
     steps: